Many hydrometallurgical processes are known and employed for the beneficiation of contaminant-containing metal-bearing ores to render said ores more suitable for metallurgical uses. However, one feature common to most, if not all, of these processes is the treatment of the metal-bearing ore with an aqueous mineral acid solution such as aqueous sulfuric, hydrochloric, nitric or phosphoric acid solutions and the like to effect a separation of contaminant values in the ore from the desired metal values in the ore. By such treatment, either the contaminant values are dissolved selectively from the ore to effect the desired separation or both the contaminant and the desired metal values are dissolved from the ore in which event the desired metal values are subsequently recovered from the aqueous acid solution by means such as, for example, hydrolysis.
A typical example of the hydrometallurgical processing of contaminant-containing metal-bearing ores is the beneficiation of iron-containing titaniferous ores for producing synthetic rutile. In the manufacture of synthetic rutile, an iron-containing titaniferous ore such as, for example, ilmenite is first subjected to reductive roasting in the presence of a reducing agent. The reduced ore then is leached with an aqueous mineral acid solution under conditions of elevated temperature and pressure to either selectively dissolve only the iron values in the ore or both the iron and the titanium values in the ore. In the event both the iron and the titanium values in the ore are dissolved upon leaching with the aqueous mineral acid solution, the titanium values then are recovered by means such as, for example, hydrolysis.
Whether only the iron values or both the iron and the titanium values are dissolved is determined by the concentration of the aqueous acid solutions employed. Thus, in processes which employ acid solutions having a free acid content of below about 30% of the total weight of the acid solution, the separation of the iron and titanium values in the ore is effected by selective dissolution of only the iron from the ore. See for example U.S. Pat. No. 3,787,139. By contrast, processes employing acid solutions having free acid contents equal to or greater than the above amount will result in the dissolution of both the iron and the titanium values. In these latter processes the final separation of the dissolved iron and titanium values is then accomplished by hydrolysis to precipitate the titanium values, as titanium dioxide, from the solution. See for example U.S. Pat. No. 3,518,054.
Most commercial hydrometallurgical processes for the manufacture of synthetic rutile effect the separation of the iron and titanium values in the titaniferous ores by means of dilute acid solutions. In such processes, the dissolution of the iron values from the ore generally is carried out under conditions of elevated temperature and pressure such that fairly reasonable rates of dissolution can be achieved. In addition, some mechanical means for agitating the ore/acid mixture is usually provided for, since it is known that agitation will also provide for increased dissolution rates. However, even under the most favorable conditions of temperature, pressure and agitation, dissolution times of at least about 12 or more hours are required to remove a substantial amount of the iron values in the ore and provide a residue, i.e., a synthetic rutile, containing 90% by weight or more of titanium dioxide.
Such protracted dissolution times not only increase the unit costs for manufacturing synthetic rutile but also reduce the production capacity for any given production facility. As illustrated by the manufacture of synthetic rutile, there exists a need for reducing the time required for the beneficiation of metal-containing ores in order to lower costs and increase production. The present invention provides such means.